Proposed work for the comingyear will consist mainly of characterizing taurine transport in isolated renal tubules of the flounder (Pseudopleuronectus americanus) and in the dogfish shark (Squalus acanthias). Preliminary studies indicate that, in contrast to the mammalian and other higher vertebrate kidneys, taurine in plasma is concentrated within renal tubule cells and then diffuses into the lumen. Thispresumably is an osmoregulatory adaptation to excrete taurine during acclimation to dilute sea water when taurine is released from tissues such as the heart, brain, skeletal muscle and erythrocytes that helps maintain a constant cell volume. In vitro experiments will include studies on the time course of taurine uptake, sodium and energy-dependence, and the influence of chloride-free medium, ouabain and 2, 4 dinitrophenol. Also to be included will be potassium-free medium, probenecid, beta-alanine Na2S2O3, furosomide, Na2SO4 and methyl glucoside, the latter to test for diffusion into the intercellular spaces and the possible uptake via the luminal sides of the cell. A kinetic analysis will seek to affinity, capcacity, saturability, and the degree of specificity of this unique taurine transport system.